The present invention generally relates to methods of inducing crystallization in thin films. More particularly, this invention relates to methods of inducing crystallization in thin films at low temperatures without causing undue damage to a substrate of the thin film.
Many thin film applications require a limited amount of defects within the thin films such as grain boundary and point defects. For example, the conversion efficiency of thin film solar cells depends on the crystallinity of photovoltaic (PV) materials (e.g., cadmium telluride (CdTE), copper indium selenide (CIS) and copper indium gallium selenide (GIGS)) that form the light absorbent layers of solar cells. Defects in the photovoltaics degrade the photon-electron conversion efficiency and transportation of electrons.
Traditional crystallization techniques used in the thin film industry, such as Rapid Thermal Annealing (RTA) techniques, have several limitations. These limitations can include issues regarding non-selective heating, slow crystal growth, temperature control for large crystal growth, and the need to use costly vacuum/inert gas environments. In particular, traditional crystallization techniques are performed in environments at between 200° C. and 600° C. Thin films are generally formed of one or more layers that are deposited on a substrate structure. Therefore, these processes are not suitable for thin films that are formed on a substrate with a melting temperature below these operational temperatures, for example, polymers.
In view of the above, it can be appreciated that there is a need for crystallization techniques that overcome one or more of these limitations, for example by being faster, more selective or lower cost. In particular, there is a need for crystallization techniques that operate at low temperatures without damaging a substrate of the thin films.